Incomplete DominanceCodominanceMultiple Alleles

What is Allele?

Homologs appear alike in the microscope. but they may have different versions of genes,called alleles, at corresponding loci (for example, an allele for freckles on one chromosome and an allele for the absence of freckles at the same locus on the homolog). Homologs are not associated with each other except during meiosis.

Alleles, alternative versions of a gene

Keep in mind!!!!

A somatic cell has two copies of each chromosome (forming a homologous pair) and thus two alleles of each gene. which may be identical or different. This figure depicts a homologous pair of chromosomes in an F 1 hybrid pea plant. The chromosome with an allele for purple flowers was inherited from one parent and that with an allele for white flowers from the other parent

Review: Dominant/Recessive

• One allele is dominant over the other (capable of masking the recessive allele)

PP = purple pp = white Pp = purple

Review Problem: Dominant/Recessive

• In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants.

P

p

P p

pp

Pp

Pp

PP- PP (1); Pp (2); pp (1)- ratio 1:2:1

- purple (3); white (1)- ratio 3:1

GENOTYPES:

PHENOTYPES:

Incomplete Dominance• A third (new) phenotype appears in the

heterozygous condition.

• Flower Color in 4 O’clocks

RR = red rr = white Rr = pink

Problem: Incomplete Dominance

• Show the cross between a pink and a white flower.

- Rr (2); rr (2)- ratio 1:1

- pink (2); white (2)- ratio 1:1

R r

r

r

rrRr

rrRr

GENOTYPES:

PHENOTYPES:

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Alel Kodominan

• Pada kasus dominan penuh dan semidominan ada salah satu alel atau gen dalam pasangan tersebut tidak berfungsi normal biasanya yang disebut resesif.

• Dalam kasus kodominan kedua alel dapat berfungsi dan diekspresikan dengan baik, tetapi produknya berbeda.

• Oleh karena itu individu bergenotip heterozigot akan memiliki fenotip campuran, bukan intermedier.

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Alel Kodominan

• Sapi merah : CRCR

• Sapi coklat :CRCW

• Sapi putih : CWCW

Bagaimana perkawinan dua ekor sapi coklat ?!

Bagaimana perkawinan sapi jantan merah dengan sapi betina coklat ? Bagaimana keturunan F2-nya ?!

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Macam Perkawinan

Banyaknya Perkawinan

Keturunan

Merah Coklat Putih

merah x merah 1/4 1/4 - -

merah x coklat 1/2 1/4 1/4 -

coklat x coklat 1/4 1/16 1/8 1/16

Jumlah 9/16 6/16 1/16

Codominance

• The heterozygous condition, both alleles are expressed equally

• Sickle Cell Anemia in Humans

NN = normal cells

SS = sickle cells NS = some of each

Types of eritrosit formed by multiple alleles

Normal cellSickle cell

Problem: Codominance• Show the cross between an individual with

sickle-cell anemia and another who is a carrier but not sick.

N S

S

S

NS

NS

SS

SS

- NS (2) SS (2)- ratio 1:1

- carrier (2); sick (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

MULTIPLE ALLELES

Genes which have more than two alleles

© 2007 Paul Billiet ODWS

Genes and their alleles

• About 30% of the genes in humans are di-allelic, that is they exist in two forms, (they have two alleles)

• About 70% are mono-allelic, they only exist in one form and they show no variation

• A very few are poly-allelic having more than two forms

© 2007 Paul Billiet ODWS

Combinations

• Di-allelic genes can generate 3 genotypes

• Genes with 3 alleles can generate 6 genotypes (3+2+1)

• Genes with 4 alleles can generate 10 genotypes

• Genes with 8 alleles can generate 36 genotypes

© 2007 Paul Billiet ODWS

Multiple Alleles

• There are more than two alleles for a trait

• Blood type in humans

• Blood Types?– Type A, Type B, Type AB, Type O

• Blood Alleles?– A, B, O (in book – IA, IB, I)

Rules for Blood Type

• A and B are codominant– AA = Type A– BB = Type B– AB = Type AB

• A and B are dominant over O– AO = type A– BO = type B– OO = type O

• http://learn.genetics.utah.edu/units/basics/blood/types.cfm

Agglutination

© Dr Delphine Grézel, Ecole Nationale Vétérinaire de Lyon

Blood types and transfusions

• People who are Type A blood produce antibodies to agglutinate cells which carry Type B antigensThey recognise them as non-self

• The opposite is true for people who are Type B• Neither of these people will agglutinate blood cells

which are Type OType O cells do not carry any antigens for the ABO systemType O cells pass incognito

• What about type AB people?

© 2007 Paul Billiet ODWS

Donor-recipient compatibility

Recipient

Type A B AB O

A

Donor B

AB

O

= Agglutination

= Safe transfusion

Note:• Type O blood may be transfused into all

the other types = the universal donor.• Type AB blood can receive blood from

all the other blood types = the universal recipient.

© 2007 Paul Billiet ODWS

Problem: Multiple Alleles• Show the cross between a mother who has type O

blood and a father who has type AB blood.

- AO (2) BO (2)- ratio 1:1

- type A (2); type B (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

O O

A

B

AO

BO

AO

BO

Problem: Multiple Alleles• Show the cross between a mother who is

heterozygous for type B blood and a father who is heterozygous for type A blood.

-AB (1); BO (1); AO (1); OO (1)- ratio 1:1:1:1

-type AB (1); type B (1) type A (1); type O (1)- ratio 1:1:1:1

GENOTYPES:

PHENOTYPES:

A O

B

O

AB

OO

BO

AO

Konon di Jepang mempelajari karakter individu berdasarkan golongan darah sudah terjadi dari tahun 1933 dilakukan oleh Furukawa Takeji. Mereka melihat kepribadian dari sisi golongan darah.

Di Jepang ada perusahaan yang hanya menerima orang-orang yang bergolongan darah A saja. Bahkan di sebuah pabrik di Jepang, 90% pekerjanya bergolongan darah A dan B, sisanya bergolongan darah O.

Alel Ganda pada Kelinci

Kombinasi Alel pada Kelinci